Blowout preventer with variable inside diameter

ABSTRACT

A variable inside diameter blowout preventer capable of sealing off a bore or around an object against high well pressures, and which may be either a ram-type preventer or an annular preventer, and wherein a plurality of anti-extrusion members are disposed for radial and circumferential movement, with the adjacent members overlapping each other, and wherein the anti-extrusion members are interlocked to move together to inhibit or prevent extrusion of a resilient sealing member therewith.

United States Patent [1 1 LeRouax [4 1 Oct. 28, 1975 BLOWOUT PREVENTERWITH VARIABLE INSIDE DIAMETER [75] Inventor: Robert K. LeRouax, Houston,Tex.

[73] Assignee: Hydril Company, Houston, Tex.

[22] Filed: Nov. 5, 1973 21 Appl. No.: 412,676

Related US. Application Data [63] Continuation-in-part of Ser. No.326,836, Jan. 26,

1973, abandoned.

[52] US. Cl 251/1; 277/127 [51] Int. Cl. E21B 33/06 [58] Field of Search251/1; 277/73, 126, 127, 277/129, 181, 185,188, 235; 166/81, 82, 84, 86,88

[56] References Cited UNITED STATES PATENTS 2,035,925 3/1936 Seamark277/34 2,246,709 6/1941 2,368,928 2/1949 King 166/10 2,609,836 9/1952Knox 277/73 2,780,294 2/1957 Loomis.. 166/203 2,846,178 8/1958 Minor251/229 X 3,038,542 6/1962 Loomis.. 166/204 3,572,628 3/1971 Jones 251/1Primary Examiner-Martin P. Schwadron Assistant ExaminerRichard GerardAttorney, Agent, or Firm-Pravel & Wilson [57] ABSTRACT A variable insidediameter blowout preventer capable of sealing off a bore or around anobject against high well pressures, and which may be either a ram-typepreventer or an annular preventer, and wherein a plurality ofanti-extrusion members are disposed for radial and circumferentialmovement, with the adjacent members overlapping each other, and whereinthe anti-extrusion members are interlocked to move together to inhibitor prevent extrusion of a resilient sealing member therewith.

13 Claims, 9 Drawing Figures Sheet 1 of 4 3,915,424

U.S. Patent Oct. 28, 1975 m IIIMJI 5%: ax

US. Patent Oct.28 1 f4 3,915,424

Sheet 3 of 4 US. Patent Oct. 28, 19 75 US. Patent Oct. 28, 1975 Sheet 4of4 3,915,424

BLOWOUT PREVENTER WITH VARIABLE INSIDE DIAMETER CROSS-REFERENCE TORELATED APPLICATIONS This application is a continuation-in-part of U.S.patent application Ser. No. 326,836 filed Jan. 26, 1973 copendingherewith, and now abandoned BACKGROUND OF THE INVENTION The field ofthis invention is blowout preventers for oil wells and the like.

Annular blowout preventers made by the Hydril Company, an example ofwhich is shown on page 2742 of the Composite Catalog for 1970-71, havebeen in extensive commercial use for a number of years. Such blowoutpreventers provide a fully-open bore there through so that drill bits,reamers, casing hangers and other large diameter tools can freely passtherethrough, but when actuated to the closed position, the packing ofeach such preventer is forced inwardly to reduce its bore andautomatically adjust its size and shape in sealing contact with whateverobject happens to then be in the bore of the preventer, thereby closingoff the annular space around such object to prevent a blowout of wellpressure from below. If no tool is in the well, the bore of thepreventer can be fully closed to prevent a blowout.

Although such Hydril blowout preventers are very satisfactory forrelatively low well pressures in the range of from about 2,000 psi. to5,000 p.s.i., it is generally desirable to use a ram type blowoutpreventer above such pressures, and above 10,000 p.s.i. well pressure,it has heretofore been considered essential to use a ram type blowoutpreventer ofa predetermined opening size because of the inability tosatisfactorily prevent extrusion of the rubber of the preventers at suchhigher pressures.

SUMMARY OF THE INVENTION The present invention relates to blowoutpreventers wherein a resilient sealing member or members are providedfor closing a well bore or sealing with a pipe or other object disposedin the bore and wherein antiextrusion means are mounted with the sealingmember or members to prevent extrusion thereof over a relatively largevariable range of bore diametersfor the preventer, and wherein theblowout preventers of this invention may be of the ram type or theannular type, and are yet capable of sealing off much higher wellpressures than with the prior known annular blowout preventers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view ofthe annular blowout preventer form of this invention, showing thepreventer in the fully open position;

FIG. 2 is a view similar to FIG. 1, but showing the blowout preventerhousing partially rotated relative to FIG. 1 and also showing thepreventer in the closed position on a pipe disposed in the well bore;

FIG. 3 is a view taken on line 3-3 to illustrate in detail the upperanti-extrusion means used with the blowout preventer of this invention;

FIG. 4 is a view taken on line 4-4 of FIG. 2 to further illustrate thedetails of the upper anti-extrusion means of this invention when in theclosed or sealing position with a pipe or other object in the well;

FIG. 5 is an isometric view of one of the antiextrusion members shown inFIGS. 3 and 4;

FIG. 6 is an isometric view of the anti-extrusion members in thesmallest diameter position corresponding to that shown in FIGS. 2 and 4;

FIG. 7 is a vertical sectional view illustrating a portion of anotherform of the blowout preventer of this invention wherein the blowoutpreventer rams are utilized;

FIG. 8 is a view taken on line 8-8 and illustrating in part theconstruction of the ram-type blowout preventer of FIG. 7, utilizing theanti-extrusion means of this invention; and

FIG. 9 is an isometric view illustrating a semicylindricalanti-extrusion means used with the blowout preventer rams of thepreventer shown in FIGS. 7 and 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, the letter Brefers generally to the form of the blowout preventer of this inventionshown in FIGS. l6. Briefly, the preventer B includes a housing H whichhas a central longitudinal bore 10 through which a pipe P or otherobject is adapted to extend in the known manner for well operations. Thehousing H is constructed so that it is positioned in a stack of blowoutpreventers or in a string of well casing or pipe in any suitable manner,as will be well understood by those skilled in the art. The blowoutpreventer B is of the annular type and it has an annular or cylindricalsealing member S formed of rubber or other suitable yieldable resilientmaterial. An upper anti-extrusion means M is provided above the sealingmember S having an annular dished out or concave inner surface 11, andthe lower anti-extrusion means M is provided below the sealing means ormember S. In the normal undistorted position of the sealing member S andthe open or expanded position of the anti-extrusion means M and M (FIGS.1 and 3) the bore provided by the surface 11 is at least as large as thebore 10 of the housing H so that the fully open bore is provided for thepassage of the pipe P and other well tools therethrough. However, uponthe application of hydraulic pressure or the like, as will be explained,the sealing member S and the anti-extrusion means M and M are urgedradially inwardly so that the well bore is closed off by the sealing ofthe member S with the pipe P. The anti-extrusion means M, as will bemore fully explained serves to prevent longitudinal extrusion of thesealing member S relative to the pipe P.

Considering the details of the blowout preventer B as shown in FIGS. l6,the housing H may take numerous forms, an example of which is shown inthe drawings and which includes a lower housing section 12 having ahousing recess 12a for receiving an annular piston 14, the sealingmember S and the anti-extrusion means M and M, as will be furtherexplained. The annular piston 14 is formed of rubber or similar materialwhich is capable of being contracted under pressure and its externalportion is exposed to pressure such as hydraulic fluid which isintroduced into the recess 12a through a fluid line 12b. Pressure isrelieved from the recess 12a through a fluid pressure line 15b which isformed in a housing section or cover 15. The cover 15 is preferablysecured to the housing section 12 by one or more bolts a (FIG. I). It isto be noted that the view of the housing H in FIG. 1 is rotatedpartially with respect to the sectional view of FIG. 2 so that in FIG. 2the connecting threaded studs 15c and 12c are illustrated and these areused for connecting the housing H in the stack of blowout preventers orin the well casing or pipe in the known manner. The bolts 15a would thusbe offset circumferentially with respect to the studs 15c.

The upper anti-extrusion means M is identical to the loweranti-extrusion means M, except that they are upside down with respect toeach other. Therefore, the details of the anti-extrusion means M will behereinafter explained and the same parts will normally be identifiedwith the same numerals and/or letters which are followed by a prime markto distinguish them from those of the anti-extrusion means M.

Considering now the upper anti-extrusion means M, such means M includesa plurality of anti-extrusion members 35 which are formed so that whenassembled together they form a cylinder or ring (FIGS. 4 and 6) andwhich are capable of moving circumferentially with respect to each otheras they move also radially from the innermost position of FIG. 6 to anopen or retracted position of FIGS. 1 and 3.

Referring now to FIG. 5 in particular, wherein one of the anti-extrusionmembers 35 is illustrated, it can be seen that each of such members 35includes a first section 35a which has an upper surface 35b and a lowersurface 35c. It is also provided with sides 35d and 35e. An interlockingrecess 3511 is also formed with respect to the upper surface 35b, aswill be more fully explained.

The surface 35c is the lower surface in the upper antiextrusion member35 and it is bonded or suitably secured to the rubber or other materialof the sealing member S so that each of the members 35 moves radially inresponse to radial movement of the material of the sealing member S.

The anti-extrusion member 35 is formed with a second section 35f whichis actually integral with the first section 35a in the preferred form ofthe invention and which generally forms a stair-stepped configurationtherewith (FIG. 5). The upper section 35f has a lower surface 35g and anupper surface 35h. The lower surface 35g is adapted to rest upon andslide relative to the surface 35b of the adjacent anti-extrusion member35.

Also, the upper section 35f of the anti-extrusion member 35 includes aninterlocking lug or projection 35k which is adapted to interflt andinterlock in the recess 35n on the adjacent anti-extrusion member 35 soas to permit circumferential movement of the adjacent members 35 whilecausing the members 35 to move as a unit radially as the inner diameteror bore of the antiextrusion means M varies from the open or retractedposition of FIG. 3 to the closed or sealing position of FIGS. 4 and 6.The innermost surface 35m of the antiextrusion member 35 is a singlesurface which is arcuate in shape so that the plurality of the members35 form an inner bore or opening defined by such surface 35m.

The anti-extrusion members 35 are assembled in an overlappingrelationship as seen in FIGS. 3 4 and 6 so that the lower surfaces 35goverlap with the adjacent surfaces 35b. Also, the interlocking lugs 35kinterfit with the interlocking recesses 35e of the adjacent members 35.Thus, the anti-extrusion members 35 function as a unit and maintaintheir ring shape even though the diameter varies'from that shown in FIG.3 to a smaller diameter down to the smallest diameter shown in FIGS. 4and 6. The overlap of surfaces 35g and 35b inhibits longitudinalextrusion of the sealing member S. Also, the overlap of the innersurface of each lug 35k with its corresponding surface in the recess 35nprevents radial extrusion of the ring 14 between adjacent members 35.

The lower anti-extrusion means M is made up of anti-extrusion members 35which are identical to the anti-extrusion members 35 except that theyare upside down with respect thereto so that the surfaces 35c aredisposed upwardly and are bonded to the rubber or other material of thesealing member S in the same manner as heretofore described inconnection with the surfaces 35c. The functioning and operation of thelower anti-extrusion means M is identical to that heretofore describedwith respect to the anti-extrusion means M.

In the operation or use of the blowout preventer B shown in FIGS. 1-6,the anti-extrusion means M and M are in the opened or retracted positionof FIG. 3 wherein the anti-extrusion members are circumferentiallyspaced from each other and have an inner bore defined by the innersurface 35m which is at least as large as the bore 11 of the sealingmember S and the bore 10 of the housing I-I. Thus, the anti-extrusionmeans M and M do not interfere with the passage of the pipe P or otherwell tools through the bore of the well pipe. The sealing member S is inits normal undistorted condition when it has the maximum open bore asshown in FIGS. 1 and 3 and likewise the annular piston 14 is in itsnormal undistorted position when the blowout preventer is in theretracted open position of FIGS. 1 and 3.

To contract the sealing member S for sealing engagement with the pipe Por other object in the well, or even upon its self in certainembodiments of the sealing member S, hydraulic pressure or other fluidis introduced into the recess 12a through the fluid inlet pipe 12b (FIG.2) to cause the annular piston 14 to contract and force the sealingmember S inwardly into sealing engagement with the external surface ofthe pipe P. Since the anti-extrusion members 35 and 35 are bonded orotherwise secured to the material of the sealing member S, they moveradially inwardly with the sealing member S and maintain substantiallythe same inner opening or bore as the sealing member S so that at alltimes they prevent longitudinal extrusion of the material of the sealingmember S. The inner surfaces 35m of the upper anti-extrusion members 35and corresponding surfaces 35m of the lower anti-extrusion members 35engage the external surface of the pipe P when the sealing members S arein contact with such pipe P so as to prevent the extrusionlongitudinally of the material of the sealing members S.

When it is desired to release the blowout preventer from its sealingposition of FIG. 2, the fluid pressure is relieved through line 15b orthrough line 12b so that the annular piston 14 returns by its inherentresiliency to the original position of FIG. 1 and likewise each sealingmember S returns to its normal undistorted position of FIG. 1, carryingwith it the members 35 and 35 so that they return to the open positionof FIG. 3.

In FIGS. 7-9, a modified form of the invention is shown wherein ablowout preventer B-l of the ramtype incorporates therewith theanti-extrusion means heretofore described in connection with FIGS. l-6,but modified so as to be semi-cylindrical for fitting with each of therams R of the blowout preventer B-l. In FIGS. 7-9, the upperanti-extrusion means is identified by the designation M-l for each ofthe rams R to distinguish from the upper anti-extrusion means M shown inFIGS. 16, and similarly the lower anti-extrusion means for each of therams R is designated M'-] in FIGS. 7-9.

The blowout preventer B-l may have any suitable type of housing such asthe housing I-I-l which is of conventional construction and which isformed with a lateral opening 50 for receiving each ram R. Upper andlower flanges 50b and 50c, having bolt openings 50d for attaching thehousing I-I-l in a stack of blowout preventers or in well casing in theknown manner are provided.

The housing I-I-l has attached thereto a conventional head or bonnet 52having a recess 52a (one of which is shown in FIG. 7) and each of whichis aligned with the lateral openings 50 in the housing H-l so as to forma continuation thereof. The rams R are received in their respectiverecesses 52a when they are in their retracted position. A piston rod 54extends through a suitable seal 52b in the bonnet 52 for each of therams R. Each piston rod 54 extends to and connects with a piston 56 ofconventional construction which is disposed in a cylinder 57 having anend cap or closure 58 secured therewith in any known manner. Forpurposes of illustration, a fluid inlet line 58a is shown forintroducing hydraulic fluid or other operating fluid into the cylinder57 for moving the piston 56 inwardly towards the center of the bore 50aof the housing I-I-l. Another fluid line 520 is provided for introducinghydraulic fluid or other fluid into the cylinder 57 for moving thepiston 56 outwardly (to the right as viewed in FIG. 1) to retract eachram R connected therewith. It will of course be understood that thepower means or piston arrangement illustrated in FIG. 7 for theright-hand ram R is duplicated for the left-hand ram R and therefore thedetails of the left-hand piston and power means are not shown.

For ease of description, the details of only one of the rams R will bedescribed hereinafter, but it will be understood that the two rams R arepreferably made in the same manner. Thus, each ram R has a ram carrier60 which is connected to the piston. rod 54, preferably in theconventional releasable manner, utilizing a button 54a fitting into asuitable slot in the ram carrier 60. In the preferred form of theinvention, the ram carrier 60 is formed of steel or other relativelyrigid material and is preferably semi-cylindrical in cross-sectionalshape (FIG. 8). The ram carrier 60 is provided with an internal recessorsurface 60a which is likewise substantially semi-cylindrical incross-sectional shape and whicn is adapted to receive a seal element 61preferably having an external convex surface 61a which substantiallyconforms with the internal surface or recess 60a-(FIG. 8). The sealmember 61 is formed of rubber or other yieldable material and it hastherewith side anti-extrusion plates 62 formed of steel or other metalwhich are adapted to engage the inside surface of an inwardly extendinglip 50f on the housing H-1.

The seal member 61 is confined at its upper end bein FIG. 7 when therams R are brought into the closed position of FIG. 7. The rams R alsoeach have a lower ram contining and alignment plate 65 with an endsurface 65a on each end of each of the plates 65 for similar contactwith each other in the closed position of the rams R as seen in FIG. 7.

It is to be noted that the vertical or longitudinal area between theupper alignment plate 64 and the lower alignment plate 65, and inwardlyof the seal member 61, forms a pocket or recess which is generallysemicylindrical for receiving the parts of the ram R of this inventionwhich are normally the primary replaceable parts. Such replaceable partsincludes a resilient yieldable sealing element or member S-] which issemicylindrical in cross-sectional shape and which is formed of rubberor other similar yieldable material. The upper anti-extrusion means M-1and the lower anti-extrusion means M-l form the other parts of thereplaceable assembly of each ram R.

Only the details of the upper anti-extrusion means M-l are fullyillustrated in the drawings, since the lower anti-extrusion means M'-]is identical thereto except that it is upside down compared to the upperantiextrusion means M-l. Thus, as best seen in FIGS. 8 and 9, the upperanti-extrusion means M-l includes a plurality of anti-extrusion members35 which are identical to those heretofore described in connection withFIGS. 3-6 and these are arranged in a semi-cylindrical form as shown inFIG. 9, with modified members at the terminal ends of the anti-extrusionmeans M-l.

Since the members 35 of the anti-extrusion means M-l are identical tothe members 35 of the antiextrusion means M, the parts thereof areidentified with the same designations and it will be understood thatthey are interrelated and function in the same manner. The end sections135 are essentially one-half sections of the members 35 and theyfunction in the same manner as can be readily seen from an examinationof FIG. 9. The anti-extrusion section 135 on the left-hand end as viewedin FIG. 9 is essentially the upper section corresponding to the uppersection 35fof each member 35 and therefore is designated as 135f and itincludes a projection or interlocking lug 135k which interfits with arecess 35e on the adjacent member 35. Only a small portion of thesurface l35c corresponding to the surface 350 is provided in suchsegment 135 and that surface 1356 is bonded to the rubber or othermaterial of the sealing member S-l.

The segment or section 135 on the right-hand end of the anti-extrusionmeans M-l as viewed in FIG. 9 is essentially the lower section of one ofthe segments 35 and is therefore identified as 135a and it hassubstantially the entire surface 135C therewith which is bonded to therubber or other material of the sealing member S-l. Its recess l35einterfits with the adjacent interlocking lug 35k in the same manner asthe other members 35 interfit and interlock.

In the operation or use of the form of the invention shown in FIGS. 7-9,the blowout preventer B is operated in the conventional manner by theapplication of hydraulic pressure or other fluid pressure to the pistons56 to move them inwardly and outwardly radially with respect to the bore50a. When the pistons 56 are moved inwardly, the rams R move towardseach other until the surfaces 64a and 65a engage each other to stopfurther inward movement of such parts and thereafter continued movementof the pistons 56 force the carriers 60 to move inwardly to contract andinwardly distort the sealing members S-l aboust the pipe P.

The anti-extrusion means M-1 and M-1 with each of the sealing members8-1 on each ram R move inwardly with the sealing member S-l asheretofore explained so that they also contact the pipe and extendinwardly beyond the inner diameter of the ram plates 64 and 65 to thusprovide a variable inner bore diameter for the rams R and to provide ametal barrier at the upper and lower ends of each seal member 8-1 forinhibiting or preventing longitudinal extrusion of such seal member S-lrelative to the pipe P.

Upon a retraction of the pistons 56 outwardly, the rams R are movedoutwardly and the seal members S-1 and their anti-extrusion meanstherewith move outwardly to return to the open or retracted positionwherein the members 35 are circumferentially spaced from each other asshown in FIG. 8. It will be appreciated that the members 35 movecircumferentially and radially as they move from the retracted positionto the inner sealing position with the pipe P so that such members 35assume a close relationship to each other and may even approach a solidsemi-cylindrical configuration corresponding to that illustrated inFIGS. 4 and 6 of the drawings for the anti-extrusion means M.

Instead of the dished out or concave surface 11, the shape of thesurface 11 or other portions of the sealing member S may be modified, orrecesses or the like in the member S may be provided, the purpose ofwhich is to compensate, or partially compensate, for the smaller volumeof the space available for the rubber of the member S when it is in itssealing position (FIG. as compared to the volume of the space availablefor such member S in its retracted position (FIGS. 1 and 9).

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape, and materials as well as in the details of the illustratedconstruction may be made without departing from the spirit of theinvention.

I claim: 1. A blowout preventer adapted to seal with a pipe or otherobject in a well bore or to close same in the absence of any object inthe well bore, comprising:

a resilient sealing member having an inner surface adapted to engage apipe or the like in a well bore;

means for urging said sealing member radially inwardly for effecting aseal with a pipe or the like in a well bore or with itself for closing awell bore;

first anti-extrusion means mounted with said sealing member and movablecircumferentially and radially therewith in response to radial inwardmove ment of said sealing member to a position contacting the pipe orobject in the well bore for preventing extrusion of the sealing memberlongitudinally when fluid pressure acts on said sealing member, saidfirst anti-extrusion means including:

a plurality of radially disposed anti-extrusion members mounted forradial movement in response to such movement of said sealing member; and

the adjacent ones of said anti-extrusion members having overlappingsurfaces, the extent of overlap of which increases as the anti-extrusionmembers move radially inward with said sealing member.

2. The blowout preventer set forth in claim 1, wherein:

said sealing member is substantially semi-cylindrical and is adapted tobe mounted as a part of a blowout preventer ram.

3. The blowout preventer set forth in claim 1,

wherein:

said sealing member is annular.

4. The blowout preventer set forth in claim 1, including:

second anti-extrusion means mounted with said sealing member on theopposite side longitudinally of said sealing member from said firstanti-extrusion means and movable radially with said sealing member inresponse to radial inward movement of said sealing member to a positioncontacting the pipe or object in the well bore for inhibiting extrusionof the sealing member longitudinally when fluid pressure acts on saidsealing member from either longitudinal direction.

5. The structure set forth in claim 4, wherein said secondanti-extrusion means includes:

a plurality of radially disposed anti-extrusion members mounted forradial movement in response to such movement of said sealing member; and

the adjacent ones of said anti-extrusion members having overlappingsurfaces, the extent of overlap of which increases as the anti-extrusionmembers move radially inwardly with said sealing member.

6. The structure set forth in claim 5, wherein:

each of said anti-extrusion members has a first portion thereof which isbonded to said sealing member.

7. The structure set forth in claim 6, wherein:

each of said anti-extrusion members has a second portion which provideswith a surface on the adjacent anti-extrusion member said overlappingsurfaces which are spaced from said sealing member.

8. The structure set forth in claim 5, wherein said secondanti-extrusion means includes:

means for interlocking said second anti-extrusion members together forradial movement together while permitting relative circumferentialmovement thereof.

9. The structure set forth in claim 1, wherein:

each of said anti-extrusion members has a first portion thereof which isbonded to said sealing member.

10. The structure set forth in claim 9, wherein:

each of said anti-extrusion members has a second portion which provideswith a surface on the adjacent anti-extrusion member said overlappingsurfaces which are spaced from said sealing member.

11. The structure set forth in claim 1, including:

means for interlocking said anti-extrusion members for radial movementtogether while permitting relative circumferential movement thereof.

12. The structure set forth in claim 1, wherein said firstanti-extrusion means includes:

a plurality of radially disposed anti-extrusion members disposed in aring and movable circumferentially relative to each other as they moveradially together;

each of said members having a lower section and an upper section in astair-stepped configuration, with the lower section bonded to saidsealing member, and with said upper section disposed away from thesealing member and slidably engaged with the adjacent anti-extrusionmember.

3 ,91 5 ,424 9 10 13. The structure set forth in claim 12, wherein eachan interlocking lug formed with said upper section anti-extrusion memberincludes: and adapted to slidably interfit with the interlockaninterlocking recess formed on the upper portion ing recess on theadjacent anti-extrusion member.

of said lower section; and

1. A blowout preventer adapted to seal with a pipe or other object in awell bore or to close same in the absence of any object in the wellbore, comprising: a resilient sealing member having an inner surfaceadapted to engage a pipe or the like in a well bore; means for urgingsaid sealing member radially inwardly for effecting a seal with a pipeor the like in a well bore or with itself for closing a well bore; firstanti-extrusion means mounted with said sealing member and movablecircumferentially and radially therewith in response to radial inwardmovement of said sealing member to a position contacting the pipe orobject in the well bore for preventing extrusion of the sealing memberlongitudinally when fluid pressure acts on said sealing member, saidfirst anti-extrusion means including: a plurality of radially disposedanti-extrusion members mounted for radial movement in response to suchmovement of said sealing member; and the adjacent ones of saidanti-extrusion members having overlapping surfaces, the extent ofoverlap of which increases as the anti-extrusion members move radiallyinward with said sealing member.
 2. The blowout preventer set forth inclaim 1, wherein: said sealing member is substantially semi-cylindricaland is adapted to be mounted as a part of a blowout preventer ram. 3.The blowout preventer set forth in claim 1, wherein: said sealing memberis annular.
 4. The blowout preventer set forth in claim 1, including:second anti-extrusion means mounted with said sealing member on theopposite side longitudinally of said sealing member from said firstanti-extrusion means and movable radially with said sealing member inresponse to radial inward movement of said sealing member to a positioncontacting the pipe or object in the well bore for inhibiting extrusionof the sealing member longitudinally when fluid pressure acts on saidsealing member from either longitudinal direction.
 5. The structure setforth in claim 4, wherein said second anti-extrusion means includes: aplurality of radially disposed anti-extrusion members mounted for radialmovement in response to such movement of said sealing member; and theadjacent ones of said anti-extrusion members having overlappingsurfaces, the extent of overlap of which increases as the anti-extrusionmembers move radially inwardly with said sealing member.
 6. Thestructure set forth in claim 5, wherein: each of said anti-extrusionmembers has a first portion thereof which is bonded to said sealingmember.
 7. The structure set forth in claim 6, wherein: each of saidanti-extrusion members has a second portion which provides with asurface on the adjacent anti-extrusion member said overlapping surfaceswhich are spaced from said sealing member.
 8. The structure set forth inclaim 5, wherein said second anti-extrusion means includes: means forinterlocking said second anti-extrusion members together for radialmovement together while permitting relative circumferential movementthereof.
 9. The structure set forth in claim 1, wherein: each of saidanti-extrusion members has a first portion thereof which is bonded tosaid sealing member.
 10. The structure set forth in claim 9, wherein:each of said anti-extrusion members has a second portion which provideswith a surface on the adjacent anti-extrusion member said overlappingsurfaces which are spaced from said sealing member.
 11. The structureset forth in claim 1, including: means for interlocking saidanti-extrusion members for radial movement together whilE permittingrelative circumferential movement thereof.
 12. The structure set forthin claim 1, wherein said first anti-extrusion means includes: aplurality of radially disposed anti-extrusion members disposed in a ringand movable circumferentially relative to each other as they moveradially together; each of said members having a lower section and anupper section in a stair-stepped configuration, with the lower sectionbonded to said sealing member, and with said upper section disposed awayfrom the sealing member and slidably engaged with the adjacentanti-extrusion member.
 13. The structure set forth in claim 12, whereineach anti-extrusion member includes: an interlocking recess formed onthe upper portion of said lower section; and an interlocking lug formedwith said upper section and adapted to slidably interfit with theinterlocking recess on the adjacent anti-extrusion member.